THIS IS A SHANNON AWARD PROVIDING PARTIAL SUPPORT FOR THE RESEARCH PROJECTS THAT FALL SHORT OF THE ASSIGNED INSTITUTE'S FUNDING RANGE BUT ARE IN THE MARGIN OF EXCELLENCE. THE SHANNON AWARD IS INTENDED TO PROVIDE SUPPORT TO TEST THE FEASIBILITY OF THE APPROACH; DEVELOP FURTHER TESTS AND REFINE RESEARCH TECHNIQUES; PERFORM SECONDARY ANALYSIS OF AVAILABLE DATA SETS; OR CONDUCT DISCRETE PROJECTS THAT CAN DEMONSTRATE THE PI'S RESEARCH CAPABILITIES OR LEAD ADDITIONAL WEIGHT TO AN ALREADY MERITORIOUS APPLICATION. THE APPLICATION BELOW IS TAKEN FROM THE ORIGINAL DOCUMENT SUBMITTED BY THE PRINCIPAL INVESTIGATOR. The goals of the proposed research are to elucidate the molecular basis of aminoglycoside ototoxicity and to develop a rational preventive treatment. Aminoglycoside antibiotics have been crucial in therapy for serious Gram-negative infections for five decades despite their ototoxic and nephrotoxic side effects. They are receiving renewed attention since opportunistic infections associated with the spread of AIDS have brought a worldwide resurgence of tuberculosis. The mechanisms of toxicity of aminoglycosides have not been established, and the absence of protective therapeutic measures continues to complicate their clinical application. The anticipated studies are based on exciting recent discoveries that allow us to propose a mechanism of toxicity and pharmacological means of intervention. The first is the discovery of a toxic 'activated gentamicin'. The activation proceeds via the formation of an iron complex as demonstrated by circular dichroism and nuclear magnetic resonance. The iron/gentamicin complex catalyzes free-radical reactions which can be inhibited by radical scavengers in vitro. Correspondingly, iron chelators dramatically attenuate gentamicin-induced hearing loss in guinea pigs in vivo. These developments enable a rational approach to the activation of gentamicin and the mechanisms of ototoxicity, and to establish hypothesis-based preventive measures of drug-induced hearing loss. The goals of the proposal will be accomplished by experiments on 1) structural analysis of the activated gentamicin and the mechanisms of its formation; 2) mechanisms of the toxic action of the activated gentamicin at the cellular and molecular level; 3) mechanisms of cell-specific toxicity; and 4) prevention or amelioration of aminoglycoside ototoxicity in guinea pigs in vivo. These questions will be addressed with well- established biochemical, physiological, analytical and physicochemical techniques. Additional information on mechanisms of toxicity and prevention will be obtained from studies of transgenic animals and of cell lines derived from a pedigree with hypersensitivity to aminoglycoside ototoxicity. The elucidation of the mechanism of aminoglycoside toxicity will provide a scientific rationale with far-reaching implications for the prevention or amelioration of adverse effects of a family of drugs whose primary efficacy is unquestioned.